Biological foundations: Heredity, Prenatal development and birth Chapter Two

In The Beginning Learning Objectives What are chromosomes and genes? How do they carry hereditary information from one generation to the next? What are common problems involving chromosomes and what are the consequences? How is a child’s heredity influenced by the environment in which they grow?

Mechanisms of Heredity Human eggs contain 23 chromosomes (threadlike structures in the nucleus) selected from the mother’s 46 one chromosome is selected from each of the 23 pairs Human sperm contains 23 chromosomes selected from the father’s 46

Mechanisms of Heredity The human egg and sperm unite resulting in a zygote -contains a complete set of 46 chromosomes - first 22 chromosomes are called autosomes -23rd pair determines the gender of the child and is called the sex chromosomes -the 46 chromosomes contain around 30,000 genes

Mechanisms of Heredity The 23rd Pair of Chromosomes -Males carry XY Chromosomes -X from mother and Y from father -Females carry XX chromosomes -X from mother and X from father

Mechanisms of Heredity Each chromosome actually consists of one molecule of deoxyribonucleic acid. (DNA) To understand the structure of DNA, imagine: Four different chemical compounds placed on two strings When two compounds (adenine, thymine, guanine, cytosine)line up exactly they make chemical compounds which are like a secrete code Each group of compounds that provides a specific set of biochemical instructions is called a gene The strings wrap around each other to create a double helix

Mechanisms of Heredity

Mechanisms of Heredity Each group of compounds that provide a set of instructions is a gene (functional unit of heredity) Fewer than 1% of genes cause differences between people Alleles – different forms of genes i.e. sickle cells (recessive) and normal red cells (dominant) The complete set of genes that make up a person’s heredity is called a genotype Phenotype - combined effect of genotype and environmental influences

Alleles Characteristics are determined my the interaction of genes on the two chromosomes in a pair Each chromosome of a pair contains one parent’s contribution to a specific trait When genes (alleles)are the same, they are call homozygous When different alleles, they are called heterozygous

Alleles Homozygous Alleles -When alleles are the same, both parents have contributed similar genes for a trait Heterozygous Alleles -The parents have contributed different versions of the trait Dominant alleles- instructions followed Recessive alleles- instructions ignored

Alleles Incomplete dominance results when one allele does not dominate another completely. The result is a trait as a sickle cell trait. In this instance the person may have tempory problems only when seriously short of O2 as when at high altitudes or when exercising.

Some Common Phenotypes Associated with Single Pair Genes Dominant Phenotype Recessive Phenotype Curly Hair Straight Hair Normal Hair Patterns of Baldness Dark Hair Blond Hair Cheek dimples No dimples Normal Hearing Some type of deafness Normal Vision Nearsightedness Farsightedness Normal color vision Green red blindness Type A or B blood Type O blood Rh positive blood Rh negative blood

Genetic Disorders Inherited disorders involve dominant or recessive alleles -Sickle-Cell Disease, PKU and Huntington’s Disease Extra, missing or damaged chromosomes result in abnormalities of development -Down’s Syndrome (extra 21st chromosome provided by the egg), Turner’s Syndrome (X),and Klinefelter’s Syndrome (XXY)

Heredity, Environment and Development Behavioral Genetics The study of the inheritance of behavioral and psychological traits. Characteristics are not either/or but are complex. Includes intelligence and personality.

Polygenetic Inheritance When many genes affect the phenotype of a trait Many psychological and behavioral characteristics are polygenetic and are impossible to trace to a single gene. Aa, Bb, Cc, Dd 4 genes can produce multiple genotypes and phenotypes. Makes study difficult. Studies easier on twins and adopted persons. Environment also plays a role. Conclusions depend on many different studies and study methods. Now can study DNA markers.

Twins Dizygotic (fraternal) twins come from two different eggs fertilized by two different sperm Monozygotic (identical) twins come from the union of one egg and one sperm that splits in two soon after conception

Twins Fraternal twins -share much of the same experience and environment - have no more genetic similarity than other siblings Identical twins -share much the same experience -genetically identical Adopted siblings have different experiences and some genetic similarity

Path From Genes to Behavior Genes impact on behavior depends on the environment -reaction range Heredity and environment interact throughout development Genes can influence the kind of environment to which a person is exposed Environment influences typically make children within a family different

Path From Genes to Behavior Genes can influence the kind of environment to which one is exposed. Niche-picking (a bright child will seek like friends etc.) – deliberately seeking environments that fir one’s heredity Environmental influences typically make children within a family different due to nonshared environmental influences.

Path From Genes to Behavior Epigenesis – interplay between genes and multiple levels of the environment from cellular level to culture Heritability coefficient – estimates the extent to which differences between people reflect heredity. Intelligence has a coefficient of 0.5 applied to specific groups of people in a particular environment. 50% of the differences in intelligence between people is due to heredity.

From Conception to Birth Learning Objectives What happens to a fertilized egg in the first two weeks after conception? When do structures and internal organs emerge in prenatal development? When do body systems begin to function well enough to support life?

Periods of Prenatal Development Period of Zygote (Weeks 1-2) From fertilization, the zygote travels down the fallopian tube dividing every 12 hours, to the time of implantation in the uterine wall. Germ disk – cluster of cells in the zygote that become the baby Period of the Embryo (Weeks 2-8) Body structures, internal organs, and the three layers of the embryo (ectoderm - hair, outer layer of skin, nervous system, mesoderm-muscles, bones, circulatory system, and endoderm- digestive system, lungs ) develop The amniotic sac fills with fluid and the umbilical cord connects the embryo to the placenta

Periods of Prenatal Development Amnion – sac containing embryo and amniotic fluid Umbilical cord houses vassals that exchange nutrients and wastes with mother’s blood Growth occurs by the cephalocaudal and proximodistal principles

The period of the zygote spans 14 days that begin with fertilization of the egg in the fallopian tubes and end with implantation of the fertilized egg in the wall of the uterus.

Periods of Prenatal Development Zygote Embryo

Periods of Prenatal Development Period of the Fetus (Week 9-38 weeks Birth) Week 9- Differentiation of the ovaries and testes, cartilage becomes bone Week 12- Circulatory system begins to function, heart has been beating almost two months Week 16- Movement felt by the mother Week 22-28- Age of viability

Periods of Prenatal Development Fetuses move – more active fetuses are more likely to be unhappy difficult babies Discern flavors Hear Remember after birth

The baby-to-be becomes much larger during the period of the fetus and its bodily systems start to work.

Conception in the 21st Century -In Vitro fertilization -inserting sperm directly into the Fallopian tubes -injecting sperm directly into the egg Inserting fertilized eggs into the womb Surrogate mothers Picking sperm donors - is this engenics (improving the human species by only allowing certain people to mate)

Principles of Growth Cephalocaudal Principle -Growth from head to spine Proximodistal Principle -Growth from areas close to the body to farthest from body

Influences of Prenatal Development Learning Objectives How is prenatal development influence by a pregnant woman’s age, her nutrition, and the stress she experiences while pregnant? How do diseases, drugs, and environmental hazards sometimes affect prenatal development? What general principles affect the ways that prenatal development can be harmed? How can prenatal development be monitored? Can abnormal prenatal development be corrected?

General Risk Factors Nutrition Stress -Inadequate maternal nutrition may result in premature birth and low birth weight. Need to increase caloric intake by 10-20% and gain25 – 35 lbs. Take additional protein, vitamins, minerals. Lack of folic acid during the first month may increase risk for spina bifida Stress -Studies show extreme maternal stress is associated with low birth weight and premature births

General Risk Factors Mother’ Age -Older mothers are more likely to have difficulty getting pregnant, miscarriages, and stillbirths -Nearly 50% of pregnancies among women in their 40’s and 50’s result in miscarriages

Teratogens Teratogen = an agent that causes abnormal prenatal development 3 categories: Drugs Disease Environmental hazards

Teratogens: Drugs Known harmful agents include: Alcohol - FAS, Aspirin – Defects in intelligence, attention, motor skills, Caffeine – rotated growth irritability Nicotine – growth and cognitive impairments Marijuana – low birth rate, less motor control Cocaine, heroin – retarded growth, irritability Fetal Alcohol Syndrome -Results from overuse of alcohol during pregnancy -Children with FAS may have mental retardation, facial deformities, and heart defects, retarded growth Leading caues of developmental disabilities in US

Teratogens: Diseases AIDS, Cytomegalovirus, Rubella (German Measles), Syphilis attack embryo of fetus directly, Chicken Pox, Chlamydia, Genital Herpes, Toxoplasmosis Aids and herpes attack as fetus passes through birth canal -Effects include: -neurological disorders -deafness -blindness -mental disability -damage to bones, eyes, ears, or heart -frequent infections -death -prematurity - miscarriage -encephalitis -damage to eyes, teeth, bones

Teratogens: Environmental Hazards Lead, Mercury, PCB’s, X-Rays -Effects may include: -mental disability -retarded growth -cerebral palsy -impaired memory and verbal skill -leukemia

How Teratogens Influence Prenatal Development The effect of the teratogen depends upon the genotype of the organism The impact of teratogens changes over the course of prenatal development Each teratogen affects a specific aspect of prenatal development The impact of teratogens depends on the dosage Damage from teratogens in not always evident at birth, but may appear later in life

Prenatal Diagnosis and Treatment Genetic Counseling Helps to assess the chances of inherited disorders Prenatal Diagnosis Ultrasound – sound waves used to generate a picture of the developing fetus – 4yh or 5yh week. Determine position ,sex, abnormalities, number Amniocentesis – needle inserted through the abdominal wall into the uterus to obtain a sample of amniotic fluid, determine genotype, danger miscarriage Chorionic Villus Sampling – sample of fetal cells obtained from a part of the placenta ,earlier 9-12 weeks, than amniocentesis, danger miscarriage

Prenatal Diagnosis and Treatment Fetal Medicine -Administering medicine to the fetus,ie.for hypothyroidism, adrenal hyperplasia, excess androgens -Fetal surgury to correct spina bifida and circulatory problems -Genetic engineering involves replacing defective genes with synthetic normal genes

Labor and Delivery Learning Objectives What are the different phases of labor and delivery? What are the natural ways of coping with the pain of childbirth? Is childbirth at home safe? What adjustments do parents face after a baby’s birth? What contributes to infant mortality in the developed and least developed countries?

Stage of Labor Stage 1 -last 12-24 hours for the first birth -contractions and enlargement of the cervix to approximately 10 centimeters,4-6 hrs for subsequent deliveries Stage 2 -actual birth of the baby -lasts about an hour first birth , 2o min subsequent Stage 3 -lasts a few minutes -expulsion of the placenta

Approaches to Childbirth Childbirth classes -Explains what happens during pregnancy and delivery -Teaches techniques to manage the pain of childbirth -natural methods, relaxation and coaching -Studies show that mothers who attend childbirth classes typically use less medication

Birthing Alternatives Home Births -less expensive -parents have more control over the conditions -birth problems are no more common at home then at the hospital when pregnancy has been problem-free Birthing Centers -more home-like then hospitals -clinic setting independent of hospital

Adjusting to Parenthood Physical changes in the woman – breasts producing milk, levels of female hormones drop, Adjustments to infants sleep-wake cycle and neeeds Father often suffers reduced attention Postpartum depression can last years affecting the child’s development

Labor and Delivery: Birth Complications Cephalopelvic Disproportion – baby’s head is larger than the pelvis; baby can’t pass through the birth canal Irregular position – shoulder presentation: baby is lying crosswise in the uterus and the shoulder appears first; breech presentation: buttocks appear first Preeclampsia – a pregnant woman has high BP, protein in her urine, and swelling in her extremities due to fluid retention Prolapsed Umbilical Cord – the umbilical cord precedes the baby through the birth canal and is squeezed shut, cutting off oxygen to the baby (hypoxia) leading to mental retardation or death

Labor and Delivery Birth Complications Hypoxia, or inadequate blood and oxygen to the baby Complications may result in a cesarean section (C-section Births before the 36th week are called premature or preterm -weighing less the 5.5 pounds (2500 grams) have low birth weight -weighing less than 3.3 pounds 1500 grams) have very low birth weight -weighing 2.2 pounds (1000 grams) or less is call extremely low birth weight

Labor and Delivery Birth Complications Birth complications can lead to aggression, violence or schizophrenia in the child Higher risk for children born into family adversity and/or poverty Excellent health care needed during pregnancy Supportive environment needed throughout childhood

Infant Mortality Infant mortality is the number of infants out of 1,000 births that die before the age of 1 year -U.S. mortality rate is just under 1%, or 7 of 1,000 -15 industrialized nations have lower infant mortality than the U.S. Possible factors include: -low birth weight -lack of free or inexpensive prenatal care -fewer paid leave of absences for pregnant women

Infant Mortality In Afghanistan 1in 6 babies die within the first year, has the highest infant mortality rate in the world In Czech Republic, Iceland, Finland, Japan odds are 1 in 300 of dying before first birthday 13 developed countries have lower infant mortality rates than US mainly because of lacking medical care, due to lack of insurance. Other developed countries have free or low cost medical care. If US reduced it’s mortality rate to 4% AS IN Europe, 8000 babies would not die annually.